pH-Induced reversible formation of core-crosslinked star polymers

Core-crosslinked star (CCS) polymers with polyethylene oxide (PEO) as a shell and crosslinked poly(4-vinylbenzylamine) (PVBA) derivatives as a core, were successfully synthesized by ‘arm-first’ method. Tert-butyloxycarbonyl (t-boc)-protected VBA (tVBA), potentially containing primary amine, was polymerized from a PEO macroinitiator by atom transfer radical polymerization to yield PEO-b-PtVBA block copolymer. The t-boc protecting groups of the resulting block copolymer were deprotected via trifluoroacetic acid (TFA) to generate PEO-b-PVBA with the primary amine functionality. The primary amine groups of PEO-b-PVBA were self-coupled in the presence of vanadium oxide (V2O5) and hydrogen peroxide via imine bond formation, leading to the CCS polymers. Dynamic light scattering results of CCS polymers showed that the hydrodynamic diameter of CCS polymers was larger than that of the initial PEO-b-PVBA block copolymer, demonstrating the successful formation of CCS polymers. Well-dispersed individual globular CCS polymers were visualized by atomic force microscopy. The imine linkages of CCS polymers were hydrolyzed at pH 4, yielding individual polymer chains. The CCS polymers were reversibly formed again above pH 8.